Japanese Patent Application Publication No. 2005-210047 describes a semiconductor device including a semiconductor substrate, trenches, gate insulating films, and gate electrodes. The trenches are provided in an upper surface of the semiconductor substrate. Each gate insulating film covers an inner surface of its corresponding trench. Each gate electrode is disposed in its corresponding trench, and is insulated from the semiconductor substrate by the gate insulating film. Further, the semiconductor substrate includes emitter regions, an upper body region, an intermediate region, a lower body region, a drift region, and a collector region. The emitter regions are regions of n-type disposed at the upper surface of the semiconductor substrate, and in direct contact respectively with their corresponding gate insulating films. The upper body region is a region of p-type that is in direct contact with the gate insulating films below the emitter regions. The intermediate region is a region of n-type in direct contact with the gate insulating films below the upper body region. The lower body region is a region of p-type in direct contact with the gate insulating films below the intermediate region. The drift region is a region of n-type in direct contact with the gate insulating films below the lower body region. The collector region is a region of p-type in direct contact with the drift region from below.
In the semiconductor device of Japanese Patent Application Publication No. 2005-210047, a flow of holes flowing from the collector region to the upper body region is suppressed by the intermediate region in an on-operation. Due to this, the holes are accumulated in the lower body region and in the drift region below the intermediate region. An increase in a concentration of the holes (that is, minor carriers) in the drift region reduces a resistance in the drift region, and a loss generated in the semiconductor device is thereby reduced.